A tap changer with a preselector and a polarity switch, with the help of which formation of gas in the insulating oil is to be reduced, is known from DE 10 2009 060 132 [U.S. Pat. No. 8,576,038]. The tap changer comprises a selector and a load changeover switch. The selector prior to a switching process initially makes power-free preselection of the new winding tap of the tapped winding to be switched over to. The switching itself is carried out by the load changeover switch. A first polarity resistor connected by a first polarity switch with a load diverter, is attached to one end of the tap winding. A second polarity resistor, which in turn is connected with the load diverter by a second polarity switch, is attached to the opposite end of the tap winding. The two polarity switches are switched on only briefly before the start of actuation of the preselector, so that the ends of the tap winding are coupled to a defined electrical potential only briefly. A disadvantage of this solution is that switching-on and switching-off of the polarity resistors can generate an arc which may cause breakdown of the insulating oil in the tap changer. Undesired chemical products can thereby arise, such as, for example, soot and gases that contaminate the insulating oil and thus shorten the service life of the tap changer or the control transformer, also termed tapped transformer.